This invention relates to an induction heating apparatus.
Among the prior art induction heating devices are included a series inverter control system in which a heating coil is connected in series with a capacitor and a parallel inverter control system in which a heating coil is connected in parallel with a capacitor. In each system, high frequency sine wave current is supplied continuously or intermittently to the heating coil for inductively heating a load, for example, a cooking pan. When controlling the power supplied to the heating coil by the inverter control system power supply voltage is subjected to phase control or rectification control using a thyristor.
Furthermore, in the prior art induction heating device the power consumed by the load varies substantially in proportion to the square of the source voltage, so that the power consumption varies as the source voltage varies. Accordingly, it is necessary to use a highly stable source. Moreover, in the prior art induction heating device, since the electromagnet energy stored in the heating coil is not returned to the source, the power efficiency is poor. Under no load condition, a surge voltage several times larger than that occurring under loaded condition is produced thus damaging the control thyristors. Furthermore, since power consumption in the load is controlled by the phase control or rectification control technique apparent power component is increased thus decreasing the power efficiency. Further, since the thyristor is used as a switching element at high voltage, the rate of rise of the current when the thyristor is turned ON is high so that a radio wave interference occurs.